Developments in microelectronics often focus on both miniaturization and integration. Miniaturization leads to electronic circuits with a high density of components having dimensions of a few nanometers on a semiconductor substrate. The integration of magnetic sensing elements is desirable for some applications.
Nanostructures have unique properties and have been investigated and used in a variety of applications such as chemical sensing, light-emitting diodes and catalysis. Magnetic nanoparticles have also been used in magnetic storage media.
Thin films with thicknesses of a few nanometers are widely used for many magnetic sensor applications, such as magnetic read heads. Magnetic sensors based on thin films typically include a stack of magnetic and non-magnetic layers as a magnetoresistive sensing element. Tuning the electrical and magnetic properties of the layers can enhance specific magnetoresistive properties of the materials such as giant magnetoresistance (GMR) and anisotropic magnetoresistance (AMR). For example, a magnetic tunneling junction (MTJ) occurs when a voltage bias is applied between two ferromagnetic (FM) layers separated by an insulating layer a few nanometers thick in an external magnetic field. The magnetic field allows the magnetization of the FM layers to be oriented, increasing or decreasing the available energy levels for electrons of different spins. When the magnetizations of the FM layers are set parallel, more electrons will flow from one FM layer to the other, decreasing the overall resistance. The variation of the resistance by this mechanism is called tunneling magnetoresistance (TMR). Because this phenomenon is sensitive to the external magnetic field it can be used as a magnetic sensing method. However, such thin-layer based technologies are typically expensive because they require multiple fabrication steps to form all the layers.
Nanostructured thin films are thin films containing nanostructures. Such films comprising metallic nanostructures embedded in a thin insulator/dielectric matrix show unique properties associated with quantum size effects, with possible applications as enhanced magnetic refrigerants, high density magnetic recording media and magnetoresistance devices.
Methods that have been used to produce magnetic nanostructured films include: molecular beam epitaxy; sol-gel deposition; plasma jet deposition; sputtering ion deposition; pulsed laser deposition; and cluster beam deposition. However, fabrication by standard methods may lack precise control over the number, size and distribution of the nanostructures. This may limit the development of device applications, because each application typically requires specific, precisely controlled properties, including thermal, chemical and magnetic characteristics, and nanostructure shape, size, stability and non-toxicity.
Ion implantation techniques are well-known for semiconductor doping. Nanostructures have been produced by ion implantation followed by vacuum annealing. However, ion implantation or deposition techniques typically use a high metal concentration, which increases the fabrication costs.
Embedded nanostructures have been made using ion implantation. But the amplitude and speed of the magnetic response of such materials is reduced by the embedding matrix. The matrix cannot be perfectly diamagnetic. The matrix can also reduce the speed of changes in the magnetic orientation of the nanostructures, mainly due to magnetoelastic coupling of the nanostructures with the matrix.
Accordingly, it is an object of the present invention to go some way to avoiding the above disadvantages; and/or to at least provide the public with a useful choice.
Other features of the invention may become apparent from the following description which is given by way of example only.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.